Conventionally, attempts have been made to widen directivity of speaker systems (see for example, Japanese Utility Model Application Publication No. Hei. 4-59696 (page 1, FIG. 1)). FIG. 26 is a longitudinal sectional view of a conventional wide dispersion speaker system 201.
In this speaker system 201, a panel 210 having an opening 211 is disposed forward relative to a diaphragm. The opening 211 is formed concentrically with a speaker unit 202. A diffuser 204 of a droplet shape is disposed forward relative to the opening 211.
The opening 211 of the panel 210 has an area smaller than that of the diaphragm of the speaker unit 202. In other words, an apparent opening area of the diaphragm of the speaker unit 202 is restricted by the panel 210. Such a restricting element (panel 210 having the opening 211) is capable of widening directivity in contrast to a construction in which only the diffuser 204 is disposed forward relative to the diaphragm.
There has been disclosed a speaker system comprising a panel having a center opening and being entirely provided with a number of circular holes is disposed forward relative to a diaphragm (see for example, Japanese Patent Application Publication No. Hei. 8-331684 (page 2, FIG. 1). Because of a number of circular holes formed over the entire panel, the panel does not substantially produce a restricting effect, and as a result, sufficient directivity is not obtained.
While the speaker system 201 using the panel 210 as a restricting member is illustrated in FIG. 26, directivity is in some cases not sufficiently widen with this structure. Especially in medium and high sound areas, desired directivity is in some cases not obtained.
In order to widen the directivity in the medium and high sound ranges without substantial change in the structure of the speaker system 201 having the structure in FIG. 26, the opening 211 of the panel 210 may be configured to have a smaller diameter. However, it may be anticipated that if the area of the opening 211 is reduced excessively, i.e., the apparent opening area of the diaphragm is restricted excessively, then an acoustic energy generated in the speaker unit 202 is not sufficiently radiated to outside. This imposes a limitation on reduction of the area of the opening 211 of the panel 210 to widen the directivity.
Meanwhile, a cover is mounted to an instrument body directly mounted to a flat portion. By way of example, in a ceiling-embedded speaker system directly mounted to a ceiling face, a speaker system body is mounted to an opening of a ceiling wall, and a cover is mounted from forward (below) to cover a front face of the speaker system body.
FIG. 27 is a conventional cover mounting structure. A ceiling wall 370 has a circular opening, and a speaker system body 310 having a speaker unit 311 is mounted into the opening. The speaker system body 310 mainly includes the speaker unit 311 and a mounting element 315. The mounting element 315 is provided with a circular hole (not shown) at a center section thereof. A diaphragm of the speaker unit 311 mounted to a rear face of the mounting element 315 is configured to be visible through the circular hole. The mounting element 315 with the speaker unit 311 mounted to the rear face thereof is secured to the ceiling wall 370, thereby allowing the speaker system body 310 to be directly and securely mounted to the ceiling.
A sound-transmissible cover 340 is mounted to the mounting element 315 so as to cover a front face of the speaker system body 310.
A plurality of body engagement portions 320 are formed at positions of a peripheral edge portion of the mounting element 315. In addition, cover engagement portions 350 are formed at positions of a peripheral edge portion of the cover 340 so as to correspond to the body engagement portions 320.
When the cover 340 is mounted to the speaker system body 310, the cover 340 is first fitted to the speaker system body 310 such that the body engagement portions 320 are close to the cover engagement portions 350, and then, the cover 340 is rotated. This causes the cover engagement portions 350 to be moved to be positioned on the body engagement portions 320, and engagement between them (body side engagement portions 320 and the cover engagement portions 350) is accomplished.
FIGS. 28(a) to 28(c) show a state in which the body engagement portion 320 and the cover engagement portion 350 are going to engage with each other step by step. FIG. 28(a) shows a state in which engagement is going to start. FIG. 28(b) shows a state before engagement is accomplished. FIG. 28(c) shows a state in which engagement is accomplished. When the state of FIG. 28(b) transitions to the state of FIG. 28(c), a protrusion 353 of the cover engagement portion 350 moves over a protrusion 327 of the body engagement portion 320. When the engagement is accomplished in the state (c), engagement between them (the body engagement portion 320 and the cover engagement portion 350) is not released unless a large rotational force is applied to the cover 340. Therefore, in a normal use condition of the cell-embedded speaker system, the cover 340 does not disengage from speaker system body 310.
When an operator is going to mount the cover 340 to the speaker system body 310, the operator may leave them in the state of FIG. 28(b). This is because, for example, when an upper end of the cover 340 is in contact with a ceiling face, the operator must apply a large force to the cover 340 to cause the state of FIG. 28(a) to transition to the state of FIG. 28(b), and the cover 340 is firmly secured even in the state of FIG. 28(b). So, the operator may assume mistakenly that the engagement between the engagement portions (the body engagement portion 320 and the cover engagement portion 350) is accomplished even in the state of FIG. 28(b), and may finish an operation in the state of FIG. 28(b).
If the cover 340 and the speaker system body 310 are left in the state of FIG. 28(b), the cover 340 may disengage from the speaker system body 310. In particular, when the speaker unit 311 is driven, the speaker system body 310 or the cover 340 vibrates, and the cover 340 gradually rotates in a direction to disengage from the speaker system body 310. Finally, the cover 340 may fall off from the speaker system body 310.